Reprinted from Real Answers SHOULD YOU STOP PUTTING AIR IN YOUR TIRES? Volume 8, Issue 3
www.trucktires.com 1-800-543-7522 ©2003, Bridgestone/ Firestone North American Tire, LLC • Real Answers, Volume 8, Issue 3
ask the DOCTOR
Should you stop putting air in your tires
As much as we preach inflation pressure maintenance, that might seem like a ludicrous question. What’s behind it, though, is the issue of whether or not air is the best thing to use for inflating tires. Lately, there’s been more and more interest is using other gases, like nitrogen. Unfortunately, there’s also a certain amount of bogus information out there regarding nitrogen as well. We’ll try to provide some “real answers” regarding nitrogen’s potential.
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©2003, Bridgestone/ Firestone North American Tire, LLC • Real Answers, Volume 8, Issue 3
ask the DOCTOR
Is nitrogen inflation new?
How does that happen?
It’s been used on giant off-highway tires, on aircraft tires, and on racing tires for many years.
Air migrates through rubber. Truck tires can lose 2 psi per month as a result of air passing through their sidewalls – like a balloon that shrivels up, but much slower. That’s why regular inflation pressure checks are a must. Even if there’s nothing “wrong,” you can still be losing pressure. And, when oxygen passes through rubber, it can come into contact with steel cords, causing them to rust too. Between aging rubber and corroding steel cords, oxygen reduces retreadability.
Off-highway tires, aircraft tires and racecar tires have used nitrogen inflation for quite some time.
Why did they switch?
Air is about one-fifth oxygen, and oxygen, especially at high temperatures and pressures, is a very reactive element. When oxygen reacts with things, the process is called oxidation. When oxidation is extremely rapid, the process is called “burning.” That’s one reason nitrogen is used in off-highway and aircraft tires. These tires run so hot they can actually catch on fire. Because air can Nitrogen doesn’t support combustion, so migrate through sidewalls, truck tires can lose nitrogen-filled tires don’t add fuel to the flames. up to 2 psi per month, And, nitrogen helps prevent slower forms of even when valves and oxidation too.
AIR: 78.1% Nitrogen 20.9% Oxygen 1% Other Gases
How does nitrogen help?
While both nitrogen and oxygen can permeate rubber, nitrogen does it much more slowly. It might take six months to lose 2 psi with nitrogen, compared to just a month with air. And, nitrogen is far less reactive. It doesn’t cause rust and corrosion on steel or aluminum, and it doesn’t beads seal properly and there are no punctures. degrade rubber. Wheel surfaces stay smooth and clean, rubber remains supple and resilient. Inflation losses are minimized – and retreadability is enhanced. Are there other benefits to nitrogen inflation?
What are those?
Oxygen corrodes aluminum and steel wheels. And, oxygen reacts with rubber, in a sense, “corroding” it too. Rust and dust from wheels can clog valve stems, causing them to leak. And, rough surfaces on wheel flanges and tire beads may not seal properly, causing additional leaks. Oxygen also ages the innerliner, that thin layer of rubber inside the tire whose function is keeping air away from the carcass. As the innerliner ages, more and more air molecules can pass through it, causing more pressure losses.
Small bits of corrosion from wheels can prevent valves from seating properly, leading to loss of air pressure.
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The air around us is full of water vapor. It’s called “humidity.” Compressing air concentrates the water in it. Draining water from your air lines every day helps, but unless you have a really efficient air dryer, chances are there’s lots of water in your compressed air.
0 psi
120 psi
When you compress air, it takes up much less volume, but the percentage of water by volume is greatly increased.
What’s the harm in that?
Water vapor in compressed air acts as a catalyst, accelerating rust and corrosion. Water vapor also absorbs and holds heat. And, when it changes from liquid to vapor, water expands tremendously in volume. So, tires inflated with wet air tend to run WATER + HEAT hotter and fluctuate in pressure more. That’s =VAPOR why racing tires, where fractions of a psi can radically change handling, are inflated with dry nitrogen.
Benefits of Nitrogen Inflation
• Less inflation pressure loss • Less inflation pressure fluctuation with heat • Reduced wheel corrosion • Longer tread life • Improved retreadability Where would we get nitrogen?
Some people use high pressure cylinders or big containers of liquid nitrogen as their source, but several companies now offer machines that separate nitrogen from air. These machines can produce nitrogen that’s 95 percent or more pure, taking it from the inexhaustible supply in the air around us.
Is nitrogen inflation cost-effective?
That’s going to depend on your situation. If your trailers go out and don’t come back for six months or more, being able to keep consistent inflation pressures may greatly lengthen tread life. Some tests have shown increases of up to 26 percent. Less rubber aging and tire cord rust could also yield a higher proportion of retreadable casings – and casings that can survive more retread cycles. That cuts cost per mile too. There’s nothing you can do that is better for your tires than maintaining the right inflation pressure – all the time. Nitrogen could help you do that. We’ll keep you posted on developments in this area.
Do we have to do something special to fill our tires?
While dry nitrogen is available from welding supply shops, there are also machines that will extract nitrogen from air.
Parts N2 + Parts other gases
Not really. If you take a truck tire that’s just been mounted, and inflate it with 95 percent nitrogen, you’ll end up with a concentration of about 93 percent nitrogen in the tire. That’s good enough to do the job.
add Nitrogen
95 + 5
add Nitrogen
95 + 5
add Nitrogen
95 + 5
add Nitrogen
95 + 5
add Nitrogen
95 + 5
add Nitrogen
95 + 5
add Nitrogen
95 + 5
to “Empty” tire 80 + 20
Why wouldn’t it be 95 percent?
745 + 55 Total: = 800 parts
Because the tire was full of air. So there was some oxygen in it before you added the nitrogen.
745 parts nitrogen ÷ 800 parts all gases = 93% nitrogen
What do we do when we’re out on the road?
Chances are, as it becomes more popular, you’ll find nitrogen inflation equipment at truckstops. But in the meantime, consider this: With nitrogen inflation, you won’t need to “top off” your tires nearly as often – or as much. And, if you do need to add pressure, the little bit of air that you might put in will have very little effect. If you have nitrogen inflation capability at “home,” when trucks come in, you can let the air out of their tires and re-inflate them with near-pure nitrogen. That will bring the concentration of nitrogen inside your tires back to optimum levels.
When you take an “empty” tire and add enough 95 percent pure nitrogen to bring its pressure up to about 105 psi, the nitrogen concentration inside ends up being about 93 percent.
4 ©2003, Bridgestone / Firestone North American Tire, LLC • Real Answers, Volume 8, Issue 3
